Study of subterranean biodiversity of the upper Neretva River catchment in Bosnia and Herzegovina

The Dinarides in the Western Balkans host a globally exceptional subterranean biodiversity, but still areas remain with little or no data on subterranean species. In this work, we present the study of subterranean fauna in the upper Neretva River catchment (Eastern Bosnia and Herzegovina), which included the first systematic exploration of the interstitial habitats in the country. During the five-day »Neretva Science Week« in the summer of 2022, we sampled six gravel bars, six springs and one cave. We gathered 268 records (taxon-locality-date) of 116 taxa, with 35 records referring to 27 terrestrial taxa. Nine terrestrial taxa were sampled in a cave, while 19 were found in aquatic samples, mostly from springs. 27 taxa were identified as obligate subterranean (troglobiotic) species, one terrestrial beetle from the cave, and 26 aquatic species, belonging to water mites, snails, and crustaceans. Eight of the aquatic troglobionts present the potential for new species to science. Of the latter, four species were distinguished based on morphology: two species of snails from the families Hydrobiidae and Moitessieriidae, one representative of Ostracoda and one Copepoda. Individuals of the aquatic troglobiotic isopods and amphipods were analysed molecularly, and based on molecular differences, two new species within the genus Proasellus and two within the genus Niphargus were proposed. Further work on all these taxa is needed for the formal descriptions of the new species to science. Despite the short study period, we have shown that the area is rich in endemic groundwater fauna. The hydroelectric power plant constructions planned in the region threaten groundwater communities by altering subterranean habitats and their connectivity. Further studies are needed to properly highlight the great diversity of the subterranean habitats of the Neretva River catchment and its wider region, and to include this knowledge in conservation strategies.